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Thromboembolic events in younger women exposed to Pfizer-BioNTech or Moderna COVID-19 vaccines

Maurizio Sessa1, Kristian Kragholm2, Anders Hviid1,3

  • 1Pharmacovigilance Research Center, Department of Drug Design and Pharmacology, University of Copenhagen, Copenhagen, Denmark.

Expert Opinion on Drug Safety
|July 15, 2021
PubMed

Insights

mRNA COVID-19 vaccines like Pfizer-BioNTech and Moderna show no increased risk of blood clots in women under 50. This safety finding is comparable to hormonal contraceptive use.

Area of Science:

  • Immunology
  • Pharmacovigilance
  • Epidemiology

Background:

  • Concerns exist regarding thrombotic risks of certain COVID-19 vaccines (e.g., Vaxzevria, Janssen).
  • The safety of mRNA vaccines (Pfizer-BioNTech, Moderna) is crucial, particularly for younger women, a priority vaccination group.
  • Understanding comparative thrombotic risk is essential for public health vaccine recommendations.

Purpose of the Study:

  • To evaluate the thrombotic safety of Pfizer-BioNTech and Moderna COVID-19 vaccines in women aged 50 years and younger.
  • To compare the risk of thromboembolic events associated with mRNA COVID-19 vaccines versus hormonal contraceptive use.

Main Methods:

  • Utilized US Vaccine Adverse Event Reporting System (VAERS) and FDA Event Reporting System (FAERS) data.
  • Analyzed thrombosis cases in women aged ≤50 following vaccination or hormonal contraceptive use.
  • Employed the reporting odds ratio (ROR) to measure disproportionality.

Main Results:

  • Out of 13.6 million women vaccinated with Pfizer-BioNTech or Moderna, 61 cases (68 events) of thrombosis were reported (1 per 222,951).
  • No disproportionate reporting of thromboembolic events was observed for the mRNA COVID-19 vaccines.
  • Thromboembolic event reporting for mRNA vaccines was not higher than for hormonal contraceptives.

Conclusions:

  • mRNA COVID-19 vaccines demonstrate favorable thrombotic safety profiles in younger women.
  • The risk of thromboembolic events associated with mRNA vaccines is not disproportionately higher compared to hormonal contraceptives.
  • Findings support the continued use of mRNA COVID-19 vaccines in women under 50.

Keywords:
COVID-19FAERSVAERSVaccinethrombosis

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